1. Field of the Invention
The present invention pertains to penetrating instruments for penetrating walls of anatomical cavities and, more particularly, to penetrating instruments having mechanisms for indicating entry of the penetrating instruments into the anatomical cavities.
2. Discussion of the Prior Art
Penetrating instruments are widely used in medical procedures to gain access to anatomical cavities ranging in size from the abdomen to small blood vessels, such as veins and arteries, epidural, pleural and subarachnoid spaces, heart ventricles and spinal and synovial cavities. Use of penetrating instruments has become an extremely popular and important first step in endoscopic, or minimally invasive, surgery to establish an endoscopic portal for many various procedures, such as laparoscopic procedures in the abdominal cavity. Such penetrating instruments typically include a cannula or portal sleeve and a penetrating member, such as a trocar, disposed within the cannula and having a sharp tip for penetrating an anatomical cavity wall with the force required to penetrate the cavity wall being dependent upon the type and thickness of the tissue forming the cavity wall. Once the wall is penetrated, it is desirable to protect tissue or organ structures in forming the cavity from inadvertent contact with the sharp tip of the penetrating member in that, once penetration is achieved, the lack of tissue resistance can result in the sharp tip traveling too far into the cavity and injuring adjacent tissue or organ structures.
A disadvantage of many prior art penetrating instruments is that they do not provide surgeons with an incremental or progressive indication of entry into the anatomical cavity during the penetrating procedure. As a result, surgeons have been forced to estimate when the sharp tip of the penetrating instrument has penetrated through the anatomical cavity wall and how far the tip protrudes into the cavity in order to determine when to reduce or remove the force applied to the penetrating instrument during penetration. In the case of small cavities, in particular, slight errors in estimating the progress of entry into an anatomical cavity can lead to the sharp tip of the penetrating member traveling too far into the cavity causing severe complications.
The penetrating instruments described in U.S. Pat. Nos. 4,186,750; 4,215,699; and 5,352,206 are representative of prior art penetrating instruments that make use of ports to communicate fluid pressure within an anatomical cavity to indicating devices, such as whistles or membranes, located at the proximal ends of the penetrating instruments. Unfortunately, penetrating instruments of this type merely confirm the presence of a penetrating member within an anatomical cavity and cannot provide a progressive indication of entry into the anatomical cavity during the penetrating procedure.
Other penetrating instruments employ complicated arrays of pressure sensors or transducers to provide an indication of the progress of an instrument during the process of penetrating an anatomical cavity wall. These include U.S. Pat. Nos. 4,299,230; 4,356,826; and 4,535,373.